1. Field of the Invention
The invention relates to a method and an apparatus for treating substrates in a rotary installation, in particular for the uniform barrier coating of plastic containers in a rotary installation.
2. Description of Related Art
The processes for coating mass-produced products, such as for example food or pharmaceutical packaging material, plastics drinks bottles, etc., require high throughput with a high coating quality for industrial manufacture.
The plastics materials which are more and more often being used for these products have barrier coatings in order to reduce their permeability to gases and liquids and to protect them from chemical attacks or UV radiation. In this context, by way of example, it is of interest to deposit thin SiOx coatings or coating systems on polymer substrates, in order to reduce their permeability in particular to oxygen and water vapor and in particular at the same time to maintain the transparency of the material.
Coatings of this type can if appropriate also usefully be applied to glass vessels or glass substrates, for example in the field of pharmaceutical packaging products, in order to prevent the migration of alkali metal ions out of the glass.
The CVD (chemical vapor deposition) process, which can be used to produce very thin and uniform layers from a wide range of gas mixtures, has proven a particularly effective and inexpensive technique for the coating of substrates.
In general very thin, uniform layers can be produced under a low thermal load in particular by means of plasma impulse CVD processes, which makes these processes particularly suitable for plastics substrates. A further advantage of the pulsed plasma-enhanced processes consists in the fact that, by way of example, very pure inorganic barrier layers can be produced, since here, unlike with the processes with unpulsed plasma excitation, undesirable organic reaction products can be removed in the interpulse period, which means that a significantly lower level of organic constituents is incorporated in the layers.
For a coating process on substrates, such as for example a barrier coating on PET bottles, to be economical, it is necessary to realize very high throughputs. Typical throughputs required are approx. 10 000 bottles per hour.
To enable the required high throughputs to be realized, inter alia rotary installations are used, in which a plurality of coating stations for the products to be coated rotate on a circular path. In this case, the individual process phases during a revolution are assigned defined circle segments or angle regions.
An apparatus of this type is known, for example, from WO 00/58631, in which 20 identical treatment stations are arranged on a carousel conveyor. The distributor arrangement with a predetermined arrangement of openings defines the sector of the rotor in which a defined process phase takes place in a treatment station. The distributor arrangement comprises two coaxial rings, namely a stationary ring and a rotating ring. The rotating ring includes openings, which are each connected to a treatment station. The stationary ring has slots, each of which has a row of openings of the rotating ring on its path, so that a treatment station passes through the process phases in angle-referenced fashion. Therefore, it is not possible to vary the process sequence in any way.
This has an adverse effect in particular in the event of disruptions and fluctuations in the process sequence, since it is not possible to react flexibly to such events, which can lead to a drop in the quality of coating.